Identifying structure and function of karst aquifer system using multiple field methods in karst trough valley area, South China

The Xiangxi River basin, South China is a steep terrain that hosts an extensive karst aquifer system with rapid subsurface runoff. The karst networks are best developed in Cambrian carbonates along the NNW and NNE directions, congruent with the predominant orientations of fissures, the permeability tensor, surface features, and flow channels. Tracer tests define a fast subsurface flow component with a maximum velocity of 240–1055 m/h that discharges to multiple outlets at high water levels, and a slow flow component with a velocity of 15 m/h at low water levels. A theoretical response model defined the response times of four karst springs as being only 5 and 8 h for hydrographs and conductivity curves, respectively. Also, a mean recession coefficient of 0.032 1/h for the fast flow component was determined by spring recession analysis. A conceptual structural model of the karst aquifer system explains the multiple flow outlets at high groundwater levels and the extensive development of highly connected karst conduits in Upper Cambrian strata.